Phillips said he will be watching places such as Lytton and Lillooet, where the hottest temperatures ever recorded in B.C. were set in 1941 when the mercury hit 44.4 C.
"This is Phoenix air coming northward. Temperatures could very well see 40, 42 degrees in the Interior," he said.
The July 1 heat wave is rare for B.C., and comes at the end of a weeklong wet spell Phillips calls the "June gloom."
"Typically about, you know, four out of every five July 1sts are wet, and temperatures can be a little on the cool side," he said. "To get a temperature above 27 and dry, about once in 76 years. What a great end to this wet spell. It's really extreme, in a way."
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Environment Canada reports a ridge of high pressure now moving over the centre of the province, which will bump up temperatures on the coast and in the Interior.
Across B.C. beginning Sunday, afternoon temperatures will rise by a few degrees each day, peaking at nearly 40 C in some areas on Tuesday or Wednesday. In the sun, Phillips said, it could be seven or eight degrees hotter.
Vancouver's warmest ever July 1 was in 1942 when temperatures soared to 30.6 C.